The effect of the type and the concentration of the lipophilic surfactant on the stability and release kinetics of the W/O/W multiple emulsions

Stable multiple emulsions that contain different lipophilic surfactants in the internal aqueous phase have been formulated. The multiple systems were assessed by evaluating several parameters such as macroscopic aspect, droplet size, percent release and accelerated stability under centrifugation or elevated temperature. The effect of polymeric and monomeric surfactants on the release mechanism and stability was examined. An excess of monomeric surfactant in the oil phase enhances the release rate and decreases stability. The release rate can be decreased by an increase of the lipophilic surfactant concentration. It appears that the more the oil globule swells, the less hydrosoluble drug is released. As a result a high swelling capacity is associated with better stability.